Exchange of Carboxylic Acids

The exchange of carboxylic acids with water occurs slowly at room temperature, and is acid catalyzed. A list of the conditions or rates of exchange of all carboxylic acids reported to the end of 1960 is given in Table V. Anions of carboxylic acids do not appear to exchange with water in neutral or basic solution except under very drastic conditions. 

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Esterification and Oxygen Exchange of Carboxylic Acids. J. Amer. chem. Soc. 61, 2584 (1939). 

THERMODYNAMIC PARAMETERS FOR THE ACID-CATALYZED "O-EXCHANGE OF CARBOXYLIC ACIDS IN WATER... 

There is some competing decarboxylation of the ethanoic acid, but the conversions in this kind of reaction are usually good. The key steps in the reaction probably are exchange of carboxylic acid groups on tetravalent lead, cleavage of the Pb-O bond to give the carboxylate radical, decarboxylation, oxidation... 

This is the general mechanism for acid catalyzed oxygen isotope exchange of carboxylic acids and esters, esterification, ester hydrolysis, and amide hydrolysis (see Vol. 10). 

The Kinetics of Exchange of Carboxylic Acid Derivatives (R—C—X) with Water... 

Solid esters are easily crystallisable materials. It is important to note that esters of alcohols must be recrystallised either from non-hydroxylic solvents (e.g. toluene) or from the alcohol from which the ester is derived. Thus methyl esters should be crystallised from methanol or methanol/toluene, but not from ethanol, n-butanol or other alcohols, in order to avoid alcohol exchange and contamination of the ester with a second ester. Useful solvents for crystallisation are the corresponding alcohols or aqueous alcohols, toluene, toluene/petroleum ether, and chloroform (ethanol-free)/toluene. Esters of carboxylic acid derived from phenols... 

At the end of the incubation period the fermentation culture mixture is adjusted to pH 2 with concentrated hydrochloric acid, the solid material present is removed by filtration, and the filter cake is washed with water. The washings are combined with the main filtrate, adjusted to pH 7.0, and 15.5 liters of the filtered culture liquid is introduced into a columnar exchanger d /a" i.d.) packed with 380 ml of carboxylic acid resin which has been preliminarily washed in succession with two liters of an aqueous solution of 37.5 grams of sodium hydroxide and with two liters of water. The column containing paromomycin is washed with two hold-up volumes of water and is eluted with 0.5 N hydrochloric acid. 

Kasai, Y., Tanimura, T., Tamura, Z., Tanimura, T., and Ozawa, Y., Automated determination of carboxylic acids by anion-exchange chromatography with specific color reaction, Anal. Chem., 49, 655, 1977. 

Tanaka, K., Chikara, H., Hu, W., and Hasebe, K., Separation of carboxylic acids on a weakly acidic cation-exchange resin by ion-exclusion chromatography, /. Chromatogr. A, 850, 187, 1999. 

Hajos, P., and Nagy, L., Retention behaviors and separation of carboxylic acids by ion-exchange chromatography, /. Chromatogr. B, 717, 27, 1998. 

The kinetics of deuterium isotope exchange between diphenyl phosphine and t-butylthiol have been studied by H n.m.r. spectroscopy.274 A negative temperature coefficient was observed for the reaction of a perf1uoroalky1 phosphite with a fluorinated aldehyde.275 The kinetics for the reaction of alcohols with phosphoryl trichloride bore strong similarities to those of carboxylic acid derivatives.276 An interesting report desribed the solvolysis of ary 1 hydroxymethyl-phosphonates. It was shown that a phosphoryl group does not prevent carbocation formation on an immediately adjacent carbon atom.277... 

Figure 4.7 Anion exchange separation of carboxylic acids in red wine. Column, Shodex C811, 100 cm x 7.6 mm i.d. eluent, 3 mM perchloric acid flow rate, 0.9 ml min-1 temperature, 60 °C detection, reaction detection using chloro-phenol red at 430 nm. Peaks 1, citric acid 2, tartaric acid 3, malic acid 4, succinic acid 5, lactic acid 6, formic acid and 1, acetic acid.

Weak cation exchange resins (carboxylic acid type) have been widely employed for the isolation and detection of marine PSP s. However, the less basic gonyautoxins (GTX s) tended to elute with the solvent front with these resins — especially when very crude... 

At ambient pH values, NOM is negatively charged, primarily due to the presence of carboxylic acid groups. Therefore, bulk NOM primarily acts as a cation exchanger. This means we may expect that negatively charged organic species will sorb more weakly to NOM than their neutral counterparts. Nevertheless, in situations in which... 

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